<!DOCTYPE html>
<html>
<head>
<script>
function changeText(id, newText) {
  var node = document.getElementById(id);
  node.childNodes[0].nodeValue = newText;
}
</script>

  <meta name='viewport' content='width=device-width'/>
  <style>
    body {
      margin: 0px;
    }
  </style>
</head>

<body>
  <button type="button" id="tap_button" onclick="changeText('tap_button', 'updatedValue')" style="width:100px;height:100px">oldValue</button>
</body>

</html>

